Researcher eyes eyespot, soil-borne wheat virus

Washington State University Extension cereal pathologist Tim Murray shared information on two wheat plant pathogens during the Spokane County Crop Improvement Association. Regional autumn weather is ideal for eyespot. So far, soilborne wheat mosaic virus may be limited to a relatively small part of Washington, but farmers who suspect they may have the disease should contact WSU's diagnostic clinic.

Eyespot, also known as strawbreaker foot rot, causes a yellow-brown discoloration on the wheat stem base. Other pathogens can also cause similar discoloration, Murray said, but eyespot creates eye-shaped lesions and can cause wheat lodging.

The disease survives in wheat straw. In the fall, when temperatures drop to 40-50 degrees, rain splashes the fungi’s microscopic spores onto other plants.

The disease grows into the stem, destroying structural tissues.

Pacific Northwest autumn weather is typically ideal for the disease, Murray said. The fungus is widespread, but most common in higher rainfall areas. Snow cover slows disease development.

Multiple lesions cause the greatest damage to the stem, cutting off nutrients to the top of the plant.

The disease is caused by two species of fungi. Sometimes both can be found on the same stem.

Planting resistant wheat varieties is the preferred method of control, Murray said, but not all resistance genes are equally effective against both species.

Murray recommends taking a representative sample from a field and spraying a foliar fungicide if five of 50 stems have lesions.

The disease is more severe in fields that were sown early, which makes for larger, more susceptible plants.

Soil-borne wheat mosaic virus is a relatively new disease in the state. The infection occurs in the fall and symptoms appear in the spring, then fade. Plants appear to recover, but the damage is done, Murray said.

The virus is transmitted by a “soil-borne fungus-like organism” that lives in the soil.